A filter structure designed to be inserted in a suction air conduit and adapted to be connected to a suitable vacuum dusting tool has been used in the past. An example of such a device is disclosed in U.S. Pat. No. 2,613,254, issued Oct. 14, 1952, in the name of White. This patent discloses a housing adapted to be connected to the dusting tool hose of a vacuum cleaner. The housing includes a cover pivotally connected to the housing and having a perforated plate inclined within the housing against which a filter sheet rests. The cover may include a transparent insert so that the accumulation of dirt upon the filter may be visualized as the cleaning operation progresses. After a short period of cleaning operation, the vacuum cleaner is shut off and the cover is moved to the open position to allow removal of the filter sheet so that a prospective purchaser may have visual evidence of the dirt which was removed by the dusting tool.
The problem with such devices is that the vacuum cleaner must be turned off in order to remove and insert the filter element. Also, the transparent section is not large enough to allow adequate visual inspection of foreign matter collected on the filter.